Modern highway tractor-trailer rigs are now equipped with air-activated brake systems which incorporate certain structural features required by the government and the trade. One important requirement imposed by regulation FMVSS-121 is that the parking brakes have to be set on the tractor and the trailer by a single control, i.e., a parking valve (hereinafter known as "PV") when parking the rig. Another important requirement is a control, now embodied in the commonly used tractor protection control valve (hereinafter known as "TPCV") which plugs the tractor system from leakage through the trailer connections during "bob-tail" tractor operation, or when rupture of a tractor-to-trailer air line occurs. In order to maintain operator use of brake controls as simple and foolproof as possible, it is desirable, if not essential, that a PV (parking valve) set the brakes of a "bob-tailed" tractor as well as the full rig in spite of some circuitry complications arising out of the inclusion of a tractor protection control valve in the system.
During the years 1975 and 1976, it was recognized that air brake systems conforming to regulation FMVSS-121 having only a TPCV and a PV, permitted a rig to roll freely if parked on an incline if an attempt was made to pressurize the trailer system. It was found during pressuring up that all brakes of the rig were released at an intermediate pressure and, unless the operator was in the seat ready to use pedal control, the rig was free to roll. At this stage of development, a trailer fill valve (hereinafter known as "TFV") was designed and incorporated into a system already containing the TPCV and the PV so that the trailer air system could be filled while the tractor brakes were securely set during the pressuring up operation. The TFV (trailer fill valve) currently used takes the prior art form shown in FIG. 1. Hence, a truck operator now has mounted within easy reach, three valves consisting of a TPCV, a PV, and a TFV. The valves present to the operator three push/pull handles. When the system comprises a TPCV as shown in FIGS. 2 and 3, a PV as shown in FIGS. 4 and 5, and a prior art TFV as shown in FIG. 1, road operation requires that the handle of the TPCV and the PV be pushed down while the TFV handle be pulled out.
With a view to making the brake system as foolproof as possible, it is an essential object of the invention to provide an air brake system for tractor-trailer rigs which includes the three above indicated valves mounted in juxtaposition, such as in a module, on which the handles of all valves may be in similar positions during normal operation of the rig. For example, valves with push/pull control motion with fully pushed-in positions for road operation are preferred.